<!doctype html>
<meta charset=utf8>
<style>
  div {
    transition: --my-property steps(2, start) 100s;
  }
</style>
<div id=div></div>
<script>
let style = document.createElement('style');
style.textContent = `
  @property --my-property {
    syntax: "<angle>";
    inherits: false;
    initial-value: 0deg;
  }
  `;
document.documentElement.append(style);
getComputedStyle(div).getPropertyValue("--my-property");
style.remove();
</script>
